This invention generally relates to an electronic system, and more specifically, to a method and devices in electronic system for powering and dissipating heat.
Present day advances in the circuit designs have allowed for increased component density in high power distribution systems, more particularly in the application of an automotive distribution box. In such cases it is desirable to have a large number, approximately more than 20, electronic power switching devices mounted on a single circuit board. This requirement of having a large number of electronic power switching devices mounted in a single circuit board poses not only a packaging problem, but also requires effective power distribution and thermal management of the power distribution systems.
Typically, when products use through hole leaded electronic power switching devices, the predominant solution has been to place the electronic power switching devices that stand perpendicular to the circuit board around the perimeter of the circuit board in close proximity to the electronics module case. Electronic power switching devices of this component package type are provided with metal tabs to remove heat from the semiconductor die. These metal tabs are in addition to the plastic case of the device. Additionally, these power switching devices are provided with leads for electrical connection. The electrical connections are exclusively made to the electronic devices through the leads of the devices that are soldered to the circuit board. The leads protrude through holes in the circuit board, therefore; the term through hole leaded device is used. In order to remove the heat generated by the electronic devices, an electrically insulating but thermally conductive material is placed between the power device tab and a heat sink area of the product module case. In order to provide a good thermal conduction, the tabs are securely pressed against the case with the help of spring clips. This method of attaching the electronic device to a circuit board does not utilize the center region of the large circuit board. This application is best suited for a relatively small number of power packages.
In case of products using surface mount devices (SMD), the SMD are frequently placed in the interior of the rectangular circuit board. In cases where the devices operate at a low power, the device does not require additional heat sinking. In many low to mid power cases where additional heat sinking is required an area of the copper is provided on the component side of the circuit board to spread heat from the SMD. In this case the copper area may or may not electrically connect to the circuit board trace sourcing current to the SMD depending on application specific current usage and application specific circuit board layout constraints. Finally, in many mid power applications the copper area under and around the SMD tab includes conductive vias (solder filled plated through holes) to the other side of the circuit board where another copper area provides further thermal conduction and may even be pressed against a silicon pad to a flat plate heat sink on the bottom side of the product case. However, these products are able to provide limited power output which is typically not enough as required in a power distribution system.
Mounting a large number of electronic power switching devices on a single circuit board not only poses a problem of distributing current to the SMDs, but also needs an effective way to remove the heat generated by the SMDs. Only stamped or milled circuit board layers would provide sufficient current conduction for the common drain circuit but that would prohibit routing of the fine pitch control traces to the pins of the SMD devices (and to the gate drives, processor area, input circuitry, etc.). Therefore, an above board electrical bus was required to route power to the devices. At the same time the package would be required to dissipate more heat than in previous applications studied. Therefore, there is a need in the industry to have a device that not only distributes current to the large number of SMDs on the circuit board but also effectively removes the heat generated by the SMDs.
In an aspect of the present invention, an electronic system having a large number of electronic components that can draw power from a common source and simultaneously dissipate heat to the common source is disclosed.
The electronic system comprises a housing having a base and a lid. A circuit board is installed on the base of the housing. At least one solder pad is disposed on the circuit board for receiving an electronic component. The solder pad provides both an electrical connection and a mechanical support to the electronic component. The electronic system is also provided with a device that is capable of distributing power to the electronic components and also removing heat away from the electronic components. The device is in contact with the solder pad and positioned adjacent to the electronic component.